Casteau is a village in Hainaut, in the Walloon region of Belgium. With the other villages Chaussée-Notre-Dame-Louvignies, Horrues, Naast, Neufvilles, Soignies, and Thieusies, they compose the municipality of Soignies.
The village is located between the towns of Mons and Soignies on the road Mons-Brussels. The river Obrecheuil flows through the village. In the past, there were some watermills along the river.
Postal code: 7061
Province: Hainaut
Municipality: Soignies
Demonym: Castellois
Elevation: 63 to 115 m
Area: 11,11 km²
Time zone: UTC+1